In a magnetron anode, an anode surrounds a central cathode. The anode is of a segmented structure having a plurality of annular segments stacked together along its length. Each annular segment includes a strap, the strap being distributed substantially along the entire axial length of the anode vanes. This enables mode separation to be achieved, even for long anode lengths and, hence, permits high power operation to be achieved. In addition, the segmented structure of the anode gives a mechanically robust design.